1. Field of the Invention
The present invention relates to an integral control system for an engine and an automatic transmission, for executing a control to reduce the output torque of the engine at a shifting time.
2. Related Art
In a vehicle having an automatic transmission mounted thereon for executing shifts by applying/releasing frictional engagement units, the output torque of an engine is reduced at the shifting time so as to reduce the shift shocks, to shorten the shifting time and to improve the durability of the frictional engagement units. This torque reducing control is generally performed by controlling the angular delay in the ignition timing of the engine because of its high responsiveness. However, the reduction in the engine torque to be achieved by the angular delay control of the ignition timing is relatively small. When the ignition timing is delayed, the exhaust gas is deteriorated to raise a load upon the exhaust cleaning system.
In the prior art, therefore, there has been developed a technique for reducing the engine torque at a shifting time by lowering the throttle opening. One example of this technique is disclosed in JP-A-3-157560. The invention, as disclosed, is applied to an engine which is equipped with an electronically controlled sub-throttle valve upstream of a main throttle valve acting with the accelerator pedal. Simultaneously with the start of the shift control, the sub-throttle valve is so throttled that the engine torque may not change. At the instant when the start of an inertia phase is detected, the sub-throttle valve is further throttled to reduce the engine torque. From the instant when it is decided that the inertia phase ends or comes to an end, the sub-throttle valve is gradually opened to increase the engine torque.
In the aforementioned control system of the prior art, the degree of opening of the sub-throttle valve is lowered according to the start of the shift control. The drop of this degree of opening so responses to the degree of opening of the main throttle valve as to cause no change in the engine torque. As a result, the engine torque is substantially reduced by further throttling the sub-throttle valve after the start of the inertia phase so that the drop in the engine torque will never fail to become considerably large. As a result, if the timing of the execution of the control of reducing the engine torque is off; the engine torque so highly drops in the torque phase that it causes a drop in the output torque, thereby resulting in shift shocks.
In order to eliminate this disadvantage, the start of the inertia phase has to be accurately detected, and the opening of the sub-throttle valve has also to be lowered. These necessities raise another disadvantage that a control of extremely high accuracy is demanded.